The invention discloses a stewing process for preparing wood dissolving pulp by utilizing natural-color unbleached papermaking-grade wood pulp in a modifying way, overcoming the defect of poor reaction property of products prepared by an alkali refining method. The stewing process conditions of natural-color unbleached wood pulp in a stewing device are as follows: liquor ratio is 1:2.5-7.0; alkali charge includes 10-50% of NaOH and 0.1-50% of Na2S; a temperature increasing condition comprises the following steps of: increasing temperature to 115-130 DEG C for 30-60 minutes, and keeping the temperature for 30-120 minutes; continuously increasing the temperature to 135-150 DEG C for 30-60 minutes, and keeping the temperature for 120-180 minutes; after the temperature is kept, continuously increasing the temperature to 165-175 DEG C, and keeping the temperature for 30-180 minutes; after the temperature is kept, reducing the temperature, and discharging; and stewing to end after the discharging. The wood pulp produced by the stewing process not only has higher content of alpha-celluloses, but also has good reaction property, and is suitable for filament and staple fibers.